HELP! Which part is the problem?

Last night I came home from work and my wife showed me that the computer had stopped responding. Get your detective hat on, here's what I saw:

1. Black screens on both monitors. They were turned on and plugged in, but they were receiving no signal from the computer. The LED lights on both were on their orange "sleep" colors, rather than their blue "on" colors. The monitors looked like the computer was stuck in its hybrid sleep/hibernation mode (in Windows 7). But all the fans were still whirring and the computer's main blue LED by the power button that flashes in sleep mode was a steady on.

2. The mouse's LED lit up when I clicked it, but it didn't stay on after the click, and it didn't wake the computer. No lights were on on the keyboard (number lock, caps lock, etc.), and it was unresponsive -- it wouldn't wake the computer. BTW, anytime we normally sent the computer to sleep (hybrid mode), a mouse click or keyboard tap would wake it -- it didn't this time.

3. The only way I get the computer to do anything was to press and hold the power button for three seconds to do a hard shutdown. When I powered up again, all the fans start whirring (CPU, GPU, PSU, case), the optical drive did its startup chatter, and the hard drives sounded like they spun up, too. But that's it. No motherboard BIOS screen, no hard drive chatter to start up the OS. I tried this a couple times. Nothing. Just blank screens, whirring fans, and idle hard drives.

What the heck is going on? Is the motherboard dead? Does something need to be reset somehow, or simply replaced? The motherboard would be my first guess, but is it by chance the RAM or the CPU? I don't believe it's the hard drives, but I could be wrong.

Oh, last thing, there's a single green LED on the motherboard itself that is steady on when I turn the power on. I don't know if that was always on before or if I'm just noticing it now. FYI, here's a list of the relevant parts (all bought from Newegg in 2009/2010):

Like I said, mouse, keyboard, and HD all appear unresponsive. Oh, on the infrared remote control detector (plugged into a USB slot) the red LED was a steady on, which was odd. It should only blink quickly when I press a button on the remote. The constant-on LED made me think there might be an error (with the motherboard? especially since it's a USB port).

Also, normally when I start up, there's a red LED on the computer for HD activity that goes crazy while the HD does its thing. But now, there's isn't any audible HD chatter, and there's zero red LED activity to indicate the HD is loading anything. The HDs are spinning, but I haven't seen that red LED blip once since yesterday.

Again, no BIOS on startup, no error codes, no nothing. I found out the little battery on the motherboard was dead, so I replaced that last night. During our move last week when I unplugged everything, it lost track of the date and time, so I had to reset those in the BIOS when I hooked it back up a week ago, but it always started up just fine since then -- until yesterday.

This is called a no POST situation. The computer is not passing its Power On Self Test, so while components are getting power, there's no control behind that power (that's why the fans spin, lights light up, etc.)

Unfortunately, these are hard to troubleshoot, but I'll try to go through the most likely scenarios for an older computer first, especially for ones that moved recently.

Likely root causes:

1. Short Circuit: Something, somewhere is causing the board to short circuit. This can be down to a small piece of conductive dust, so clean the computer thoroughly with canned air. It could also be a screw shorting against the case or a rubbed wire, etc. so that can be tricky to test. Any rattles in the case need to be tracked down.

2. Power supply failure: Something in the power supply let go-- typically when you see some activity, the +5v line works, but the +12v line is toast. Likely a blown fuse or bad capacitor. If you have a spare power supply to test with, plug that in and you can determine if the existing power supply is the culprit. Note: A blown capacitor on the board is not likely as you have solid state capacitors on the motherboard. You can look to buy a replacement or look to buy a power supply tester (I recommend replacement, but keep the receipt.)

3. Loose power connector: You can see these symptoms if the auxiliary +12v power connector has worked loose (the blue 4-pin connector diagonal from the CPU socket) Also possible would be video card power connectors being loose if the card you have has any auxiliary power connectors.

4. Something's not plugged in all the way: CPU's unlikely here, but RAM and video cards are likely. You say that you checked the video card, though. Could also be component failure.

5. Bad motherboard (this is bad news as AM3 is no longer made. You could get AM3+, but then you're throwing money away on an older CPU without a good upgrade path (AMD's Vishera is OK if you can tolerate high power/heat, but most of the rest of their CPUs since the Phenom II have been duds.) If you have to buy a board, consider a complete replcement with something like an i5-3570K and thank your lucky stars you live near a Microcenter So to troubleshoot:

1. Check with 2nd PSU (tip: It's easy to lay the 2nd PSU on top of or next to the case and just leave the existing one in)

2. Take the board down to bare minimum components possible (to see if anything's not plugged in properly if a 2nd PSU doesn't solve the problem. Start with board, CPU + power. It may beep or go through self-test stuff, but it should be responsive to the power/reset switches. Then add in RAM one stick at a time and then the video. If it works at that point, with nothing else connected, the basic computer is probably good and some connector or component is bad. Likely failure here would be one of the RAM sticks.

3. Repeat the above step with the motherboard out of the case on a non-conductive surface-- just build the computer as you would but without a case. (<-- yes this is a PITA) If you need to do this, note that you can turn the system on by going to where the front panel connectors are and touching the two pins for power with a screwdriver while holding the non-conductive handle. This completes the circuit and tells the computer to start.

This smells like MB failsauce. I'd unplug/reconnect everything (unplug PS connectors, RAM, expansion cards, SATA cables, EVERYTHING but I wouldn't fark with unseating the CPU). If that doesn't do it my money is on a MB failure.

Everything was seated pretty tight before. But I unplugged the video card, RAM, hard drives, etc. (only the motherboard, CPU, PSU, and the front panel USB/SD card/power button connectors are hooked up), then I hit the power button and...no beeps whatsoever. No response. No BIOS. Just a whirring CPU and PSU fan.

As for the CMOS, I think I found the jumpers, but I'm not sure. I pulled the battery, so that should have reset it, right?

Next I have to scrounge up an old PSU from the house we just moved from (my wife threatened to leave all the computer parts behind, but now I *need* them!)

If that doesn't work, I'm headed to Microcenter for a shopping spree. I already called, and they said they'll return stuff within 30 days, even if I plugged it in and tried it out. So I might have to find the culprit piece by piece.

You should see the Frankenstein mess I have in my basement right now. I went to Microcenter, grabbed a motherboard (on sale), a PSU (on sale), a video card (on rebate), and the dirt cheapest really fast RAM I've seen in a long time.

I drove home and decided to start with the PSU. Nothing.

I didn't really think the video card was the problem (and didn't want to deal with a rebate unless it really was), so I set that aside. I was going to go piece by piece on the old board, and then I had a thought...

I wondered what would happen if I took all my old parts and threw them on the new motherboard. I've never snapped so many pieces into place so fast in my life. CPU, RAM, PSU, GPU, and HDD x2 all swapped out like I'm on a pit crew. Then I found what I thought were the two pins for the power on, and voila, it sprang to life.

Fans whirred, hard drives spun up, I held my breath. And then the first sign of life -- the LEDs on the monitors turned blue! And then there was the BIOS screen. And then the Windows login screen!

Turns out my trusty motherboard was indeed the culprit. And I'll be returning a lot of unused parts to Microcenter.

So now my only question is: how can I diagnose what exactly went wrong with the old board?

For grins pull out your old board and try what you just did with the new board (assemble your computer outside the case). Also reset your CMOS using the jumper (as Nevarre said CMOS chips can retain their state for some time now with out a battery). Either the power section of your motherboard has gone bad - I think this is less likely but certainly possible - OR your CMOS programming is corrupt and a simple resetting will restore sanity to your rig - OR your CMOS is blown (due to a power surge).

I suspect your old board will boot up just fine. I recommend a good surge protector / UPS to keep this from happening again.

Geez, people. It isn't the PSU. I don't know why so many people here always seem to think the motherboard isn't a likely point of failure. I've had as many boards die as power supplies over the years.

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So now my only question is: how can I diagnose what exactly went wrong with the old board?

Check the capacitors. If you see the tops bulging or anything that's crusted up on top, they've gone bad. You can replace them with a real steady hand and a soldering iron, but I wouldn't make that a system to count on.

Yes it can even be both. Last system I repaired (2.5 year old AMD Hex Core) required new MB and PS. Seasonic PS and Gigabyte Ultra Durable Board. Board was under warranty. PS suppose to be, but too much trouble to RMA it.

I just remembered that I never reported back what happened. So, in case anyone still cares (or is even still listening), it wasn't the motherboard, PSU, CMOS, capacitors, or video card. It was one of the two sticks of RAM. Yes, the RAM. Here's how I figured it out.

I RMA'd two motherboards in a row, thinking that by some fluke I got a bad board in return. After the second board arrived and it still wasn't working, I posted this out of desperation...viewtopic.php?f=8&t=1199717...and then I finally tried adding one part at a time. Just like Nevarre recommended above. (And just like I started to do until I decided prematurely it was my motherboard's fault.) Heh.

Anyway, I RMA'd the RAM, got two new sticks back (sweet!), and it's been working fine ever since.